Bleaching clay

Green coloration, present in many vegetable oils, poses a particular problem in oil extracted from immature or damaged soybeans. Chlorophyll is the compound responsible for this defect. StmcturaHy, chlorophyll is composed of a porphyrin ring system, in which magnesium is the central metal atom, and a phytol side chain which imparts a hydrophobic character to the stmcture. Conventional bleaching clays are not as effective for removal of chlorophylls as for red pigments, and specialized acid-activated adsorbents or carbon are required. 

The principal disadvantage of absorption bleaching is the problem of disposal of spent bleaching clay. Oil absorbed on the clay is exposed to air and is generally too oxidized to recover. Furthermore, spontaneous combustion of the oil-laden clay is a possibiUty in a landfill. Incineration of the spent clay along with sohd municipal waste to recover otherwise wasted energy is an attractive possibiUty. 

Uses. The principal uses of NaBH are ia synthesis of pharmaceuticals (qv) and fine organic chemicals removal of trace impurities from bulk organic chemicals wood-pulp bleaching, clay leaching, and vat-dye reductions and removal and recovery of trace metals from plant effluents. 

Fats and Oils. The oxidation of fats and oils in food products can be prevented by the addition of citric acid to chelate the trace metals that catalyze the oxidation. Citric acid is also used in the bleaching clays and the degumming process during oil refining to remove chlorophyll and phosphohpids (59—63). 

D. D. Brooks and co-workers, "The Synergistic Effect of Neutral Bleaching Clay and Citric Acid Chlorophyll Removal," paper presented at the... 

Bentonite is a rock rich in montmorillonite that has usually resulted from the alteration of volcanic dust (ash) of the intermediate (latitic) siliceous types. In general, reUcts of partially unaltered feldspar, quartz, or volcanic glass shards offer evidence of the parent rock. Most adsorbent clays, bleaching clays, and many clay catalysts are smectites, although some are palygorskite [1337-76 ]. 

Bleaching clay load (typically 0.1-2.0 percent) and operating temperatures depend on the type and quality of oil processed.114 Modem bleaching processes are conducted... 

Bleaching. The refined oils are usually dark in color owing to the presence of some pigmented materials such as chlorophyll or carotenoids and minor impurities like residual phosphatides, soaps, metals, and oxi-datin products. Bleaching reduces the color by absorbing these colorants on bleaching earth (bentonite clays), or activated charcoal, or both. In addition to decolorization, bleaching clay also absorbs suspended matter and other minor impurities. 

Natural bleaching clays are aluminum silicates (bentonite, atta-pulgite, and montmorillonite), containing relatively high amounts of Mg, Ca, or Fe. The clays are generally activated by heat treatment. The high metal content, however, limits the adsorptive activity of these... 

B. W. Lew, M. L. Wolfrom and R. M. Goepp, Jr., J. Am. Chem. Soc., 68, 1449 (1946). A suitable fuller s earth clay was Florex XXX it was produced by the Flori-din Co., Warren, Pa. Other selective clays were Floridin XXX (Floridin Co., Warren, Pa.), Types A and AA Attapulgus Clays (Attapulgus Clay Co., Attapulgus, Ga.), Bleaching Clay 260 (Industrial Minerals and Chemical Co., Berkeley, Calif.), and J. Neutrol (Filtrol Corp., Los Angeles, Calif.). 

After refining (neutralization), the oil is bleached. Color bodies in the oil are adsorbed on the surface of the bleaching clay and activated carbon particles. Experiments cited by Brimberg (19) showed that bleaching process follows the rate formula. In (c/cq) = —ky/i, where t is the time from the addition of bleaching clay c is the concentration of pigment at time t, cq is the concentration at to, and k is the rate constant. 

Excessive rain before harvest can increase chlorophyll content of the crude oil. There are two types of chlorophylls found in oUseed Chlorophyll-A and Chloro-phyll-B. Chlorophylls are oU soluble and produce green color in the oU. At normal concentrations, they are easily reduced in the bleaching process. It is very difficult to reduce the chlorophylls from the crude oil if it is obtained from seeds that are not mature or have developed higher chlorophylls because of excessive rain before the harvest. The normal practice is to use an excess amount of bleaching clay to reduce chlorophylls. This reduces the natural antioxidants in the oil, produces higher amounts of free radicals in the oil, and reduces its stability. 

Evaluations of spent bleaching clay as a feed supplement indicate that, for poultry diets, inclusion rates of up to 7.5% spent clay in diets produced no deleterious effects on feed intake, growth rate, or feed efficiency (101). These results suggest that spent clay could be added to poultry feed at 0.5-2.0% which is similar to the amount of bentonite clay currently used as a pellet binder in poultry diets. The metabolizable energy (ME) of spent clay was determined to be 2870 kcal/kg (dry matter basis) but would vary with oil content. Other studies have also demonstrated the feeding value of spent clay (102). 

Refinery Bleach. Various bleaching clays purify and remove color bodies from refined oils. These wastes contain 5% to 35% oil. The characteristics of these materials are such that they will combust spontaneously, which has created problems for disposal in sanitary landfills, as well as at factory locations in some instances, but this condition can be overcome by several methods. The model refinery presented in the previous section will generate about 2500 kg of waste earth per day, of which 570 kg is oil. 

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